A communication system provides for the communication of data between communication stations, of which at least one of the communication stations forms a sending station and another of the communication stations forms a receiving station. The sending and receiving stations are interconnected by way of a communication channel upon which data, originated at, or otherwise provided to, the sending station is communicated to the receiving station.
A wide variety of different types of communication systems have been developed and deployed. And, such communication systems are regularly utilized to effectuate many different types of communication services. As a result of technological advancements, new types of communication systems have been developed and installed. Additional technological advancements shall likely permit the development and deployment of additional types of communication systems providing additional, and improved, communication services to be effectuated.
Radio communication systems are exemplary of communication systems that have benefited from technological advancements and of which infrastructures thereof have been deployed and regularly utilized through which to effectuate various types of communication services. Radio communication systems differ with conventional, wireline communication systems in that the communication channel that interconnects sending and receiving stations operable therein is defined upon a radio link extending between the communication stations. That is to say, a communication path extending between the sending and receiving stations of a radio communication system includes, along at least a portion thereof, a radio link upon which the communication channel is defined. A wireline connection is thereby obviated for the portion of the communication path that, instead, is defined upon the radio link.
Use of a radio communication system through which to communicate provides various advantages. The installation and deployment costs, for example, of a radio communication system are generally less than costs required to install and deploy a corresponding wireline communication system. And, a radio communication system can be implemented as a mobile communication system in which one, or more, of the communication stations operable therein are permitted mobility, forming, as a result, a mobile communication system.
Many modern radio communication systems make use of digital communication techniques. When digital communication techniques are used, data that is to be communicated is first placed into digitized form and then, typically, formatted into data packets or frames, according to a selected formatting scheme. Once formatted, the data is modulated and transduced into electromagnetic form for communication on the radio communication channel to a receiving station. Once delivered at the receiving station, the receiving station operates to demodulate the data and recreate the informational content thereof.
If the information is communicated in a distortion-free environment, the values of the data, when received at the receiving station identically correspond in value with the values of the data when transmitted by a sending station. But, because no communication system is distortion-free, the values of the data, when received at the receiving station differ with the corresponding values of the data when sent by the sending station. If the values differ significantly, the informational content of the data cannot be recreated at the receiving station.
Communication conditions on the radio communication channel adversely affect the communication of the data. For instance, multipath communication conditions cause the data to fade during its communication upon the radio communication channel. Multipath transmission conditions are sometimes referred to as fading conditions. Fading of the data alters the values of the data, or portions thereof, such that, when detected at the receiving station, the values of the data differ with corresponding values when sent by the sending station.
Various manners are used by which to attempt to compensate for the distortion caused by fading. For instance, by increasing the diversity of the data, the likelihood that the informational content of the data can be recovered at the receiving station is increased.
Time diversity, for instance, is one type of diversity that is sometimes utilized to compensate for the effects of fading. When time diversity is utilized, time redundancy is introduced into the data. By introducing time redundancy, loss of portions of the data during its communication upon a fading channel is less likely to prevent the informational content of the data to be recovered. Fading sometimes is time-variant. And, the increased redundancy permits the loss of portions of the data due to fading of such portions less likely to prevent recovery of the informational content of the data.
Space diversity is another type of diversity that is also sometimes increased also to compensate for the effects of fading. Space diversity, typically, refers to the utilization of more than one transmit antenna at a sending station at which to transduce data into electromagnetic form for communication to a receiving station. The antennas are separated by selected by selected separation distances to provide selected levels of correlation between the data transmitted at the separate ones of the antennas. The separation distances between the antennas are generally selected to ensure that the data communicated at the respective ones of the antennas achieve at least a selected level of uncorrelation so that fading occurs in uncorrelated manners.
Space diversity is also provided at a receiver through the use of multiple receive antennas, also spaced apart by selected separation distances.
Communication systems that utilize space diversity at both the transmitter, i.e., the sending station, and the receiving station, i.e., the receiver, are sometimes referred to as being a MIMO (multiple input, multiple output) communication system. The number of receive antennas in such a system is generally, albeit not necessarily, at least as great as the number of transmit antennas formed at the transmitter. Each transmit antenna and receive antenna pair defines a separate channel that exhibits different fading conditions. The level of fading exhibited on the different channels is sometimes significant, particularly when the separate transmit and separate receive antenna transducers are highly uncorrelated. That is to say, communication conditions on a channel defined by a particular transmit and receive antenna pair might well be relatively better than communication conditions on another of the channels defined by another of the transmit and receive antenna pair.
Multiple input, multiple output communication system also advantageously provide for relatively high throughput rates as separate data can be communicated upon the different channels defined by the different ones of the transmit antenna and receive antenna pairs. As radio communication systems, such as cellular communication systems increasingly are used to effectuate data intensive communication services, MIMO implementations shall increasingly be utilized. For instance, in a CDMA 2000 communication system that provides for 1xEV-DV communication services, high data rate communication services shall be provided.
Various proposals have been set forth for MIMO implementations for use in a CDMA 2000/1xEV-DV communication system. A so-called per antenna rate control (PARC) system has been proposed by which to communicate independent data streams, albeit encoded at different ones of the transmit antennas. In this proposed implementation, side information regarding channel strengths is provided. Based upon this information, a radio base station tailors a data rate and a modulation order for each transmit antenna.
If any additional manners could be provided by which to enhance the system capacity in an MIMO system, yet further improvements in the communication in data intensive communication services would be facilitated.
It is in light of this background information related to communications in a radio communication system having a transmitter that includes multiple transmit antennas that the significant improvements of the present invention have evolved.